Lacus Iuturnae (Fig. 51): the spring-fed pool of Juturna at the south corner of the Forum Romanum between the Temple of Castor and the Atrium Vestae, where Castor and Pollux were seen watering their horses after the Battle of Lake Regillus in 496 B.C. Thereafter, the Temple of Castor was built just west of the lacus (Ovid Fast. 1.705-8; Dion. Hal. 6.13.4). This epiphany was believed to have been repeated after the Battle of Pydna in 168 B.C. (Florus 1.28.15; Val. Max. 1.8.1). The twins are shown watering their horses on coins of the Gens Postumia, to which the victor of Lake Regillus belonged, of about 96-90 B.C. (B. M. Coins, Rom. Rep. 2.310 nos. 718-23; Crawford 335 no. 10); the lacus is there shown as a low trough or puteal. Servius (Servius ad Aen. 12.139) says that Iuturna was properly the name of a spring near the River Numicus, given this name because of its salubrious water (iuvare). From this spring in ancient times water was said to have been brought to Rome for all sacrifices. A temple to Juturna was first built in the Campus Martius (see Iuturna, Templum). When the forum spring was assigned to her is not known, but its water was always regarded as especially fine and healthful (see also Varro Ling. 5.71; Frontinus Aq. 4). PA suggests that the name might also be derived from Diuturna (its being a perpetual spring).

The area was explored only in 1900. What came to light was a basin 2.12 m deep, measuring at the bottom 5.13 m x 5.04 m. In the middle of this is a rectangular base about 3 m long, 2 m wide, and 1.78 m high. This presumably held a marble group of the Dioscuri and their horses, fine work of the early classical period, which was found smashed to fragments in the basin and is now partially reassembled and on display in the Forum Antiquarium (Helbig4 2.2067). Nash, however, thinks this base is too small and would therefore like to locate the group on a pair of little squares marked on the Marble Plan on the north side of the basin (ArchCl 11 [1959]: 227-31). The basin was entirely lined with marble, and the springs emerged in the northeast and northwest corners. The walls behind the revetment are faced with reticulate, and the whole appears to be an early imperial refurbishing of a late republican treatment. Under the floor of the basin have been found extensive remains of a pavement in blocks of tufa laid on a different orientation (that of the precinct of Vesta).

At the top of the basin is a ledge, about 1.50 m wide, framed in a heavy wall of rubble masonry 1.23 m high, capped by a travertine coping with traces of the setting of a metal fence. At the top the whole measures about 10 m square. In the fourth century the east side of the basin was rebuilt in different form, apparently to create a place for the Statio Aquarum. A marble altar that was found in the basin has been set up on the intermediate ledge; on its four faces it shows the Dioscuri, Helen (as Selene), Leda, and Jupiter.

About 4 m south of the lacus, facing it at an angle, is the Aedicula Iuturnae, a pretty little shrine on a high base without a stair of approach. This must have held a statue of the divinity in the apsidal cella. Its shallow porch is framed by two slender Corinthian columns and a neat triangular pediment. In front of it, over a well, is a large marble puteal, unfluted, with an inscription commemorating a restoration by M. Barbatius Pollio, believed to be the adherent of Mark Antony (CIL 6.36807 = ILS 9261). Just in front of this and obscuring it has now been set a marble altar of Severan date commonly believed to represent Juturna taking leave of Turnus. However, the gesture is ambiguous, and it might equally well represent Mars and Venus. It is not properly in place here; it was found used as a step in a medieval stair. The aedicula is identified by an inscription on the epistyle: IVTVRNA(i) s(acrum) (NSc 1901, 74 [G. Boni]). It all but abuts on an apisidal room in which the brickwork is considered Hadrianic.

East of the lacus, between it and the Atrium Vestae, a ramp mounts to the Nova Via, and the triangular space between was filled with later construction, some of which encroached on the lacus itself, a large brick-faced vault carrying it over the basin. Inscriptions found here show that it became the headquarters of the water department of Rome, the Statio Aquarum. One, a base of a statue to Constantine, erected 1 March 328, commemorates a restoration at the time by Fl. Maesius Egnatius Lollianus, curator aquarum (NSc 1901, 129). It therefore appears that the statio had already been located here for some time. Statues of Aesculapius and Apollo found in the vicinity have been taken as evidence that it had also become the center of a healing cult, perhaps as early as the second century. Finds of pottery show that the spring continued in use as late as the eighth century, and even at present it produces water pronounced excellent by the experts.

NSc 1901, 41-144 (G. Boni), the most detailed account of the excavation and finds; BdA 40 (1955): 346-47 (A. Davico), the account of the restoration of the Aedicula Iuturnae; Nash 2.9-17, 395-97; Roma, archeologia nel centro (1985), 1.73-92 (E. M. Steinby); E. M. Steinby, Lacus Iuturnae I (Rome 1989)